from Thomas Sowell’s Basic Economics:
That cost is reflected in the market when the price that one individual is willing to pay becomes a cost that others are forced to pay, in order to get a share of the same scarce resource or the products made from it. … The real cost of building a bridge are the other things that could have been built with that same labor and material. This is also true at the level of a given individual, even when no money is involved. The cost of watching a television sitcom or soap opera is the value of the other things that could have been done with that same time.
Ouch. Substitute Sudoku for sitcom and you’ve nailed me, Thomas Sowell.